This invention relates generally to the preparation of certain Group 4 metal complexes by means of a combination amine elimination/alkylation process to produce metal complexes. More particularly the present invention relates to a novel process for conversion of initial Group 4 metal amides to the corresponding metal alkyl complexes.
The manufacture of Group 4 metal amide derivatives and subsequent conversion to the corresponding halide or alkyl metal complexes has been previously taught in U.S. Pat. Nos. 5,312,938, 5,597,935, 5,861,352, 5,880,302, 6,020,444, and 6,232,256, and elsewhere. In WO02/38628 Group 4 metal complexes containing “spectator ligands” such as amino-substituted cyclic amine compounds were prepared through a two step amine elimination/alkylation process. Suitable amide complexes for use in such process include Group 4 metal tetra(N,N-dialkylamido) compounds, especially titanium-, zirconium- or hafnium-tetrakis(N,N-dimethylamide) compounds. Suitable alkylating agents include trialkylaluminum compounds, especially trimethylaluminum, and alumoxanes.
A persistent problem of the foregoing processes is the ability to produce the intermediate diamide complex in high yield and purity. Because the initial exchange step is an equilibrium process, complete conversion generally cannot be attained even after resorting to the use of elevated temperatures and/or venting or vacuum removal of amine byproducts. A process in which complexation of the metal by a ligand is facilitated, thereby resulting in the use of lower reaction temperatures, shorter reaction times, and/or characterized by higher yields, is still desired. In addition, a process in which the multiple steps of the prior art are combined in a single unified or “one-pot” process is desired as well.